There is disclosed a method for forming a wax pattern having a hollow structure by using a die including an upper die and a lower die (see, e.g., Patent Document 1). According to this method for forming a wax pattern having a hollow structure, a desired hollow structure is formed in the wax pattern before the wax pattern is taken out of the die. Further, a hollow structure forming member is arranged at a position corresponding to the hollow structure of the wax pattern of the die, and this hollow structure forming member is made of a wax and then removed from the wax pattern. Furthermore, the hollow structure forming member has solubility, and this hollow structure forming member is dissolved and removed from the wax pattern after the wax is cured.
According to the method for forming a wax pattern having a hollow structure configured as described above, since the desired hollow structure is formed in the wax pattern when the wax pattern is removed from the die, productivity of casting manufacture in a lost wax process can be considerably improved. Moreover, when a member that is integrated with a casting is previously arranged at a position corresponding to the hollow structure of the wax pattern of the die in place of forming the hollow structure in the wax pattern, a material different from a casting material such as ceramics can be integrated with the casting.
On the other hand, there is disclosed a method for manufacturing a precision casting mold by which a surface of an evaporative pattern made of a photocurable resin and formed into substantially the same shape as a casting is coated with a refractory to form a precursor of a mold, and an oxygen containing gas is blown into the precursor at temperatures equal to or more than a decomposition temperature of the photocurable resin to combust and remove the evaporative pattern (see, e.g., Patent Document 2). According to this method for manufacturing a precision casting mold, stereolithography can be used as a method for fabricating an evaporative pattern. This stereolithography is implemented by inputting three-dimensional shape data of a casting to a computer, and irradiating a predetermined position of a photocurable resin liquid with light (a laser beam, an ultraviolet ray, or the like) based on this value to cure the resin. Additionally, a cured part is moved in a height direction, the uncured resin liquid is irradiated with the light in the similar manner to sequentially cure the resin liquid in the height direction, thereby fabricating a resin pattern. When the stereolithography is used, since a pattern is directly fabricated from the three-dimensional shape data, the pattern having a complicated shape or a small wall thickness can be highly precisely and easily fabricated, and production efficiency of the mold can be also improved.
According to the thus configured method for manufacturing a precision casting mold, since sufficient oxygen can be supplied at the time of combusting a resin, ambient oxygen concentration can be prevented from lowering with combustion of the resin. Consequently, since combustion of the resin is promoted and the greater part of the resin is combusted and removed in a short time without stopping, a stress load added to the mold by thermal expansion of the resin is reduced, and destruction of the mold can be avoided. Further, when the greater part of the resin is removed, an influence of the thermal expansion of the resin on the mold can be ignored, and hence then a residue (soot) in the mold can be completely combusted and removed over sufficient time.